When a newspaper clipping slid out of an envelope addressed to the studio Ellis wasn't particularly surprised. The studio had just been featured in the business section of the local newspaper and she figured it was someone they knew sending them a copy.

But when she unfolded the clipping, what she saw brought her to tears.

Above the photo in scrawling cursive, the stranger wrote, "I'm tired of articles espousing fitness and health while those in the picture are neither."

And in the left-hand margin: "Pictures/articles like this give others a license to be overweight or obese." It's one thing if the sender was bashing barre fitness or their business model Sisco (left) explains. But this was an attack on the women's bodies from "someone who didn't know us, had never met us, and never set foot in the studio" Sisco tells SELF.

However, Ellis and Sisco weren't about to allow hateful comments from a stranger bring them down. They were going to do something about it.

The next day, they published a blog post describing the incident, hoping to spread the message to their clients that body shaming is never okay and inspire them to stand up and say enough is enough. "Judging anyone based on their looks or a picture is just sad...and yes it is a form of bullying. It sends the wrong message to women everywhere. Women should lift each other up, not tear each other down. So nice try lady...but mission not accomplished," they wrote.

Ellis and Sisco have been very open about their personal struggles with body image in the past.

The post has since received a lot of attention, and women across the country have been calling to voice their support and share their own stories.

"It was hurtful enough to receive a piece of mail like that," Ellis says.

And while Sisco and Ellis know who sent the hate mail (the name and return address were on the envelope), they're not telling. "Putting her name out in public knowing that people would criticize and tear her down just didn't seem right to us," says Ellis. Nor would it jibe with Barre East's mission—to provide a judgement-free zone where all women can feel comfortable.

The sender hasn't taken Ellis and Sisco up on their offer to try one of their classes, but she did stop by to say she was sorry—an apology they readily accepted.

"I don't know what led her up to this point in her life that she felt it necessary to write those things about us," says Sisco. "But, honestly, I think she's done us all a favor by starting this conversation."